(1) Field of the Invention
The present invention generally relates to a file protection system for protecting various types of information (files) in a computer system from unfair use, a software utilization system using the file protection system and a storage medium such as a CD-ROM in which software is stored, and more particularly to a file protection system which can exactly detect whether files have been moved or copied from another computer system or have been altered, a software utilization system in which only authorized users can use software by using the file protection system and a storage medium used in the software utilization system.
(2) Description of the Related Art
In recent years, a software sales method has been proposed. In this software sales method, a storage medium, such as a CD-ROM or a magneto-optical disk (MO), in which software is stored in a protected state and a license (a key) used to release the software from the protected state are separately sold. For example, as shown in FIG. 1, software (applications etc.)(hereinafter referred to as a software-article-1) for which a lock 110 is set (encryption) is stored in a CD-ROM 100. The CD-ROM 100 and a key (a license) 120 used to set the lock 110 for the software-article-1 are separately sold to a user A. The key (the license) 120 which is used for a lock 121 specific to the user A is given to the user A. The lock 121 is opened (decryption) by a key 210 which is stored as a key specific to the user A in a computer system 200 (for the user A) in which software is utilized. As a result, the software-article-1 can be used in the computer system 200.
A user B may have a key 310 specific to the user B but does not have the key 210 specific to the user A. Thus, even if the user B unjustly gets the key 120, the lock 121 for the key 120 can not be opened by the user B. That is, the software-article-1 stored in the protected state as described above in the CD-ROM 100 is unusable in a computer system 300 for the user
However, if the key 210 specific to the user A and the software-article-1 both of which are stored in the com uter system 200 for the user A are copied and installed in the other computer systems, the software-article-1 can be used in other computer systems.